viii LIST OF CONTRIBUTORS Bradley Stoughton. Ph. D. Consulting Metallurgist. Iron Smelting. Hugh S. Taylor. Ph. D. Professor of Physical Chemistry. Princeton University. Reginald Trautschold. M. E. Engineering Economist. The Transportation of Solids. Edward S. Wiard. E. M. Consulting Engineer. Grading, Sizing and Screening. Separation, Concentration. R. M. Wilhelm. A. B. U. S. Bureau of Standards. Pyrometry and Thermometry.